Samsara passes in front of a cloud of glowing gas.
While the temptation is to call the background object a nebula, this would be highly unlikely. Nebulae are Huge; much larger than a solar system. If this were a nebula, then that same nebula would be visible from every planet and every part of the system, and we would have seen it before now.
So, the cloud must be some (much smaller) cloud of gas, left by a comet or collision of asteroids or similar phenomena.
Of course, the real reason to put it in is because it looks cool, but to call it a nebula would be a misnomer.
Oooo, lookit the pretty colours....